The present invention relates to a propeller shaft which is arranged in a power train (drive line) of a vehicle, and in particular, to a propeller shaft which can adjust a torsional resonance point or the like.
In general, a great vibration and a noise are generated and made in the case where torsional vibration characteristic of a propeller shaft of a vehicle is improper and a torsional resonance point of the power train and a normally rotational speed of the propeller shaft are coincident.
If a torsional rigidity of the propeller shaft is too high, it is hard to make a connection (conjunction) of a clutch between an engine and a transmission; for this reason, a starting acceleration performance of a vehicle lowers. Further, when the vehicle is in an inertia running state, a torque is not applied to the propeller shaft; for this reason, a so-called lash noise (resulting from rattling and contact of gears) is made at a portion where gears engage with each other.
In order to solve these problems as described above, there is a need of absorbing a torsional vibration of the propeller shaft and lowering a torsional rigidity so as to adjust torsional vibration characteristic.
In this related art, there are a double structure special shaft, and a torque variation absorbing fly-wheel disclosed in Japanese Unexamined Utility Model Publication No. 59-108848, etc.
The aforesaid double structure special shaft has an outer steel pipe and an inner steel pipe penetrating through the outer steel pipe. These steel pipes are connected to each other by means of rubber. Further, one and another sides of respective outer and inner steel pipes are individually connected with a coupling joint. In the special shaft, a torsional rigidity is lowered by the flexibility of rubber, so that torsional vibration characteristic can be improved.
Moreover, the aforesaid torque variation absorbing fly-wheel is called as a double mass fly-wheel. The double mass fly-wheel is composed of a pair of fly-wheels, a coil spring for connecting fly-wheels to each other, and the like. In the torque variation absorbing fly-wheel, the torsional rigidity is lowered by the flexibility of the coil spring and the inertia of both fly-wheels, so that torsional vibration characteristic can be improved.
However, in the case of the special shaft, the torsional vibration characteristic is limited depending upon a flexible rate determined by a property of rubber and a thickness thereof; for this reason, it is impossible to make a torsional angle great. Thus, a range of adjusting the torsional vibration characteristic is narrow.
In the case of the torque variation absorbing fly-wheel, the range of adjusting the torsional vibration characteristic is narrow like the case of the special shaft, and further, the structure is complicated; for this reason, the cost is high.
Neither special shaft nor torque variation absorbing fly-wheel has a function of obtaining a desired torsional vibration characteristic.
For these reasons, neither special shaft nor the torque variation absorbing fly-wheel can sufficiently solve the aforesaid problems relative to the propeller shaft.